There has been known an image forming apparatus which has a conveyance member that carries and conveys a sheet or an image, such as a sheet conveyance belt that conveys a sheet toward an image forming part (for example, which is an image transfer unit for an electro-photographic type or an ink ejection unit for an inkjet type) or an image conveyance belt that conveys an image transferred from an image forming unit. According to the image forming apparatus, in order to perform a high quality printing, it is necessary to control a traveling speed of the conveyance member to be a target speed.
For example, JP 2006-178374A describes an image forming apparatus which employs a technique of controlling the traveling speed of a sheet conveyance belt to be constant. Specifically, in the image forming apparatus, in order to adjust the traveling speed of the sheet conveyance belt, marks provided on the sheet conveyance belt are read and feedback control is performed so that a detection interval of the marks becomes constant. Thereby, the traveling speed of the sheet conveyance belt is controlled to be a target speed.
However, that image forming apparatus has the following problems. That is, according to that image forming apparatus, in order to determine whether the traveling speed of the sheet conveyance belt is appropriate, it is necessary to read the marks for traveling speed detection, which are provided in advance at end portions of the sheet conveyance belt in the width direction, and to detect a time interval between the adjacent marks. However, when there is a scratch or foreign material in any of the adjacent marks, the time interval cannot be accurately measured. Therefore, it is possible to erroneously determine whether the traveling speed is appropriate or whether the traveling speed is appropriate cannot be determined, so that the reliability is rather low.